1. Field of the Invention
The present invention relates to an apparatus for cutting a semiconductor single-crystal rod transversely to wafers by means of an inside diameter rotary blade or saw.
2. Prior Art
One conventional cutting apparatus of the aforedescribed type comprises a distance measuring device for sensing a warp of the blade caused during the cutting operation. Results of the measurement as to such warp are used, for instance, as data for computing the cross-sectional configuration of the wafers sliced from the rod-like ingot to judge their quality.
The distance measuring device is provided with a sensing head or sensor stationarily located in a fixed position opposed to one of opposite faces of the blade, and is operable to successively measure and compare the distances from the sensing head to the blade which momentarily vary due to the warp of the blade, to thereby sense the warp of the blade.
The timing for the sensing of the distance measuring device has been hitherto set so that the sensing is effected at predetermined regular time intervals. In other words, assuming that an annular portion of the one face of the blade to be opposed to the sensing head is uniformly planar, the distance between the sensing head and the annular portion has been measured at regular time intervals. As a result, that portion of the blade opposed to the sensing head at a prescribed timing has not been brought into an opposed relation to the sensing head at the next timing.
In an actual blade, however, such annular portion of the blade is not uniformly planar due to the orientation caused in the blade when it is formed by rolling. More specifically, the elongation of the blade measured in a direction of the rolling is different from that of the blade measured in a direction perpendicular to the rolling direction. Consequently, when mounted on a rotating head and stretched outwardly, the blade is subjected to such a warp that that intermediate portion of the one face disposed between inner and outer peripheral portions protrudes therefrom, and that the direction of warping in the direction of the rolling is reverse to that in the direction perpendicular to the rolling direction. Besides, the degree of the warping varies from blade to blade. The blade is thus subjected to an intricate warp and thereby to deflection or runout when rotated. Accordingly, the precision of the measurement as to the warp of the blade has been low unduly, thereby adversely affecting the judgment of the quality of the wafers sliced from the ingot.